First: The need to defrag 'frequently' is totally dependent on whether you do a lot of installs, uninstalls, picture/video uploads/downloads ... ie: lots of adding, updating and/or deleting of files = defrag needed more often.
Second: It is also dependent on whether your disk directory uses the older FAT (MS-DOS File Access Table) structure or the newer NTFS (Windows-NT File Structure) ... right click the drive, click properties, look at the general tabs 'File system:' to see what you have if you don't know. Also note, both types can, and often do, exist on one PC and even on one hard drive now days (ie: Drive 1, partition "C:/" might be FAT while drive 1, partition "D:/" could be NTFS). Lots of Windows-XP machines were/are configured by the vendors to have both FAT & NTFS directories as having some FAT space allows them to use older software/drivers.
Within limits, NTFS directories 'self defrag' on the fly. FAT directories NEVER do. Both directories can stand being defragged after lots of file updates (ie: after a windows 'service pack' is installed and tested), but FAT disk directories need defragging more often ... still typically only monthly for most users.
MS Windows defrag utility works fine (slow, pretty safe, and FREE). Several other products are faster (but at a cost usually). I use MS Win-XP defrag and "AusLogics Disk Defrag" (also free) alternating between them as I figure (for some unknown reason) that each has their own defrag formula so I may get the best of both so to speak.
1. Defrag utilities need to know where everything is on the disk drive to work. They (especially MS Windows defrag) can get confused/hung up by anti-virus/spy/adware utilities that check every file that is opened since they usually 'log' the fact that they checked the file ... which causes a directory update ... which causes the defrag routine to restart ... which causes another log update ... which causes the defrag to restart again ... and on, and on.
2. Thus: It is best if you physically disconnect from the internet (ie: power off your modem/wireless hub and/or unplug your DSL/cable/Ethernet connection) and then shut down your anti-virus/spy/adware checkers before defragging.
3. Defraggers need disk space to work (ie: 10-15% of your hard drive must be 'available/free'), so backup and/or delete what you can before you start your defrag utility.
4. Then: Start your defrag and leave the PC alone until it finishes. Defragging really works your system in very critical areas and if your PC crashes, etc., during a defrag, you can loose everything on the hard drive.
5. Today?s hard drives have good life expectancy and occasional defragging will not hurt them. Unnecessary defragging will add some wear to them, of course.
6. Thus, as always, make backups of important files.
Goodtime Charlie, VA